1. Field of the Invention
The present invention relates to a screwdriving power tool including a housing, a hollow spindle rotatably supported in the housing and driven by a motor, in particular by an electric motor. The screwdriving power tool further includes a clutch rotationally connecting, in its engagement position, the hollow spindle with the motor, and rotationally disconnecting the hollow spindle from the motor in its disengagement position, with the clutch including clutch spring means for preloading the clutch in the disengagement position.
The screwdriving power tool also includes a screwing-in spindle connected, for joint rotation therewith, with a chuck for receiving a working tool, and connected with the hollow spindle for a joint rotation therewith and for an axial displacement relative thereto, with the clutch being brought into the engagement position thereof by the displacement of the screwing-in spindle against a biasing force of the clutch springs. A percussion mechanism applies a pulsed axial force to the screwing-in spindle.
2. Description of the Prior Art
In screwdriving power tools of the type described above, during screwing-in of a fastening element, the screwing-in spindle can be displaced by the axial percussion mechanism in a pulsed manner. Thereby, e.g., a quick-action constructional screw can be screwed in, upon attachment of a constructional element formed of a soft material such as, e.g., gypsum plaster board to a metal frame after piercing the soft material, without pressing the screwdriving power tool against the hard metal frame too hard. During the screw-in process, the axial forces, which are generated by the axial percussion mechanism and which act as pressing forces, are completely sufficient for screwing a screw in metal.
German Publication DE 100 32 949 discloses a screwdriving power tool with an axial percussion mechanism that applies pulsed axial forces to a screwing-in spindle. The screwing-in spindle is retained in a hollow spindle with a possibility of a limited axial displacement by ball-shaped locking members. The ball-shaped locking members are pivotally arranged in radial receiving bores formed in the hollow spindle and permanently project in axially extending grooves formed in the outer surface of the screwing-in spindle. For transmission of the rotational movement, the screwing-in spindle should be displaced relative to the tool housing in the direction opposite the screw-in direction by pressing of the screwdriving power tool against the to-be-attached workpiece. The hollow spindle is displaced, at a certain point of the screwing-in spindle displacement, together therewith until a clutch member, which is supported on the hollow spindle, engages a clutch member fixedly secured relative to the housing.
This construction permits to produce a compact screwdriving power tool with which a good quality of a screw connection is achieved at reduced press-on forces.
However, during an operation of a known screwdriving power tool, it may occur that an axial displacement of the screwing-in spindle in the screw-in direction effected with the axial percussion mechanism, may cause a momentary disengagement of the clutch. This can result in a smaller work progress, on one hand, and in an increased wear, on the other hand. In addition, the displaceable support of the screwing-in spindle makes the insertion and removal of the working tool in and out of the chuck, respectively, more difficult.
Accordingly, an object of the present invention is to provide a screwdriving power tool with an axial percussion mechanism in which the foregoing drawbacks of the known screwdriving power tool are eliminated and which can be easily handled.
Another object of the present invention is to provide a screwdriving power tool of the type described above which would have an extended service life.